Syssarcosis is a joining between two bones made with muscle tissue or flesh. A closely related concept is syndesmosis, referring to connections between bones made with ligaments. Ligaments create stronger and sturdier joins than muscle tissue alone, as ligaments are less prone to tearing in response to stress. Many joints in the human body are connected and articulated with muscle tissue in addition to ligaments, with the muscle tissue playing a role in joint function and stability.
One area of the body where a syssarcosis can be seen is in the connection between the hyoid bone and the lower jaw. Unusually, these bones do not actually articulate with each other, as in the case of other joints like the shoulder or knee. Instead, they are connected with a network of ligaments and muscle tissue. This makes the hyoid more movable than joints where the bones directly articulate with each other; the lower jaw and upper jaw, for example, are articulated and have a fixed relationship to each other.
Muscle tissue around a joint can help stabilize it, with the syssarcosis supporting the joint, preventing it from stretching too far. People with significant muscular development will have more musculature around the joints and this can sometimes leave marks on the bone; anthropologists examining bones can learn about the musculature of the deceased person by looking for the points of muscle attachment and seeing how pronounced they are.
Ligaments may be located in and around the muscle to add stability to the joint and prevent joint injuries. The balance of ligaments and muscle tissue varies from person to person depending on sex and physical fitness. The gums are another example in the body of a joint involving syssarcosis, as the gums act to support the teeth and hold them in place. Gum loss can destabilize the teeth and put the patient at risk of using them.
Other joints in the body need to be less flexible and require firmer connections than those available with syssarcosis alone. In these cases, cartilage may be used as the connective tissue to articulate a joint. The connections between the sternum and ribs are an example. The cartilage allows enough flexibility for lung expansion, without making the chest so flexible that people could be injured by falls or blows to the chest. As people age, cartilage in these joints tends to ossify, hardening into bone, and the degree of ossification can provide important information about a person's age and level of health.